You can own more than one. You can't be the primary account holder on more than one (for the purposes of sharing digital games).
If you own two and buy games for both on separate accounts it's fine. If you're the only account holder and you want to share games you've bought with other accounts (kids account etc) on an additional system Sony doesn't allow that.
So i have my primary PS5 at home, and I'm also logged in on my brother's PS5 not as primary. Can he still play my online games? Can i download them on his primary and have him play using his account? Cos that was possible last i checked.